We have chosen IFN-gamma gene expression as a model system for analysis of the control of gene expression in T cells and large granular lymphocytes (LGL). This past year we have continued to dissect the non-coding regions of the human IFN-gamma genomic DNA to determine which regions enhance/repress gene transcription in response to extracellular signals. We have shown that the NFkappaB protein binding sites in the promoter enhance but are not essential for promoter activity and that the intronic NFkappaB binding sites can further upregulate this activity. In other studies, we have developed a model by which the DNA binding protein YY-1 can inhibit promoter activity in the absence of exogenous activation signals, thus suggesting that specific DNA binding proteins are involved in both the activation and silencing of IFN-gamma transcription. In addition to our analyses of DNA binding protein/promoter interactions, we have found that HIV infection of T cell lines producing IFN-gamma results in methylation of the IFN-gamma promoter and subsequent down regulation of IFN-gamma production, thus further substantiating our model where methylation of the IFN-gamma promoter inversely correlates with IFN-gamma gene expression. Overall, our data indicate that multiple DNA binding protein family members interact with the human IFN-gamma genomic DNA and that control of IFN-gamma gene expression involves 5' and intronic transcriptional control regions as well as DNA methylation. In addition to the studies on the transcriptional control of IFN-gamma gene expression, we have continued to analyze our transgenic mice which express IFN-gamma in the bone marrow and thymus. We have found that these mice are highly sensitive to the effects of low doses of endotoxin and the bone marrow macrophages are in a "primed" state as they produce nitric oxide after treatment with LPS alone. In addition, the T cells in these animals are defective in their proliferative response and cytokine production in response to stimulation. Studies are ongoing to characterize the biochemical/molecular.